// This is the "inner loop" of the neural simulation.
// Every spike event could cause upto 256 different weights to
// be put into the ring buffer.
static inline void _process_fixed_synapses(address_t fixed_region_address,
uint32_t time) {
register uint32_t *synaptic_words = synapse_row_fixed_weight_controls(
fixed_region_address);
register uint32_t fixed_synapse = synapse_row_num_fixed_synapses(
fixed_region_address);
#ifdef SYNAPSE_BENCHMARK
num_fixed_pre_synaptic_events += fixed_synapse;
#endif // SYNAPSE_BENCHMARK
for (; fixed_synapse > 0; fixed_synapse--) {
// Get the next 32 bit word from the synaptic_row
// (should autoincrement pointer in single instruction)
uint32_t synaptic_word = *synaptic_words++;
// Extract components from this word
uint32_t delay = synapse_row_sparse_delay(synaptic_word);
uint32_t combined_synapse_neuron_index = synapse_row_sparse_type_index(
synaptic_word);
uint32_t weight = synapse_row_sparse_weight(synaptic_word);
// Convert into ring buffer offset
uint32_t ring_buffer_index = synapses_get_ring_buffer_index_combined(
delay + time, combined_synapse_neuron_index);
// Add weight to current ring buffer value
uint32_t accumulation = ring_buffers[ring_buffer_index] + weight;
// If 17th bit is set, saturate accumulator at UINT16_MAX (0xFFFF)
// **NOTE** 0x10000 can be expressed as an ARM literal,
// but 0xFFFF cannot. Therefore, we use (0x10000 - 1)
// to obtain this value
uint32_t sat_test = accumulation & 0x10000;
if (sat_test) {
accumulation = sat_test - 1;
saturation_count += 1;
}
// Store saturated value back in ring-buffer
ring_buffers[ring_buffer_index] = accumulation;
}
}
bool synapse_dynamics_process_plastic_synapses(
address_t plastic_region_address, address_t fixed_region_address,
weight_t *ring_buffers, uint32_t time) {
// Extract seperate arrays of plastic synapses (from plastic region),
// Control words (from fixed region) and number of plastic synapses
plastic_synapse_t *plastic_words = _plastic_synapses(
plastic_region_address);
const control_t *control_words = synapse_row_plastic_controls(
fixed_region_address);
size_t plastic_synapse = synapse_row_num_plastic_controls(
fixed_region_address);
#ifdef SYNAPSE_BENCHMARK
num_plastic_pre_synaptic_events += plastic_synapse;
#endif // SYNAPSE_BENCHMARK
// Get event history from synaptic row
pre_event_history_t *event_history = _plastic_event_history(
plastic_region_address);
// Get last pre-synaptic event from event history
// **NOTE** at this level we don't care about individual synaptic delays
const uint32_t last_pre_time =
event_history->times[event_history->count_minus_one];
// Loop through plastic synapses
for (; plastic_synapse > 0; plastic_synapse--) {
// Get next control word (autoincrementing)
uint32_t control_word = *control_words++;
// Extract control-word components
// **NOTE** cunningly, control word is just the same as lower
// 16-bits of 32-bit fixed synapse so same functions can be used
uint32_t delay = synapse_row_sparse_delay(control_word);
uint32_t type = synapse_row_sparse_type(control_word);
uint32_t index = synapse_row_sparse_index(control_word);
uint32_t type_index = synapse_row_sparse_type_index(control_word);
// Create update state from the plastic synaptic word
update_state_t current_state = synapse_structure_get_update_state(
*plastic_words, type);
// Update the synapse state
final_state_t final_state = _plasticity_update_synapse(
time, last_pre_time, delay, current_state, event_history,
&post_event_history[index]);
// Convert into ring buffer offset
uint32_t ring_buffer_index = synapses_get_ring_buffer_index_combined(
delay + time, type_index);
// Add weight to ring-buffer entry
// **NOTE** Dave suspects that this could be a potential location
// for overflow
ring_buffers[ring_buffer_index] += synapse_structure_get_final_weight(
final_state);
// Write back updated synaptic word to plastic region
*plastic_words++ = synapse_structure_get_final_synaptic_word(
final_state);
}
log_debug("Adding pre-synaptic event to trace at time:%u", time);
// Add pre-event
const pre_trace_t last_pre_trace =
event_history->traces[event_history->count_minus_one];
pre_events_add(time, event_history, timing_add_pre_spike(
time, last_pre_time, last_pre_trace));
return true;
}
